The mechanism which allows anaerobes such as Bacteroides to survive the transit from stringently anaerobic conditions in the bowel through air or the oxygenated blood stream to a soft tissue infection or external trauma has not been investigated. Any anaerobe possessing even meager defenses against oxygen would more likely remain viable for greater periods than anaerobes completely devoid of those defenses and could thus be more often involved in soft tissue infections. This proposal addresses the question of function of antioxidant enzymes (superoxide dismutase, catalase) in clinically important anaerobes as correlated with aerotolerance characteristics and their role in establishing an infection. Maximum oxygen levels for anaerobe growth, bacteriostatic and correlated with cellular levels of catalase and superoxide dismutase. Catalase and superoxide dismutase levels within the anaerobe can be altered by manipulating growth conditions, and test cultures with elevated or depressed levels of those enzymes will be tested for resistance to oxygen toxicity, ability to establish a soft tissue abscess in an animal, and their resistance to kill after phagocytosis by polymorphonuclear leucocytes. Superoxide dismutase and catalase may be present at a wound or trauma site due to erythrocyte or tissue cell lysis and could protect anaerobes present at the site from oxidative stresses. This hypothesis will be tested directly by evaluating the role of catalase and/or superoxide dismutase coinjected with the test organism in generating a soft tissue abscess.